Colorectal cancer is the fourth most frequent cancer in the Western world, with about 130,000 new cases yearly in the US. Forty to 50% of all colorectal cancer patients will be diagnosed with early stage disease (Dukes' stage A or B). Most of these patients with early stage colorectal cancer can be cured by surgery alone. Thus, risk of recurrence is closely related to stage of disease at time of primary surgery, with about a 10% relapse rate in Dukes' stage A and 25–30% in Dukes' stage B. Patients with Dukes' stage C colorectal cancer have a five-year relapse rate of 70% following surgery and are offered adjuvant chemotherapy. Following relapse, the risk of dying of the disease is significant. Thus, one way to improve survival is to increase the number of patients being diagnosed with early stage disease. Screening for colorectal cancer has been shown to improve survival, however, current tests suffer from a lack of compliance, from low sensitivity, and from the need for strict dietary restrictions. Thus, the development of new and improved tests for the early detection of colorectal cancer is needed.
Because metastatic disease is the main cause of cancer patient morbidity and mortality, molecules involved in the regulation of tumor invasion and metastasis are attractive as potential diagnostic/prognostic targets. It is well established that proteolytic enzymes produced by cancer cells or by cells in the tumor stroma are involved in extracellular tissue degradation, leading to cancer cell invasion and metastasis. A number of enzymes have been associated with this process, the most thoroughly investigated being the metalloproteinases, such as the collagenases and stromelysins, and the serine proteases such as plasmin. Recently, data have been published indicating that these molecules, free or bound in complexes, are released from tumor tissue and find their way into the circulation.
Matrix metalloproteinases (MMP's) play a pivotal role in cancer growth and spread, contributing to enzymatic degradation of the extracellular matrix (Liotta et al, 1991; Stetler-Stevenson et al, 1993; MacDougall & Matrisian, 1995). The naturally occurring inhibitors of MMP's, tissue inhibitors of MMP's (TIMP's), form tight 1:1 stoichiometric complexes with the activated forms of the MMP's (Welgus et al, 1985; Kleiner et al, 1993), thereby inhibiting the catalytic activity of these enzymes (Stetler-Stevenson et al, 1996; Goldberg et al, 1992; Birkedal-Hansen et al, 1993). While the balance between the matrix-degrading properties of MMP's and the inhibitory effect of TIMP's is closely regulated under normal physiological conditions (Matrisian, 1992; Thorgeirsson et al, 1993; Birkedal-Hansen et al, 1993), this balance might be disrupted in malignant tissue.
A number of enzyme-linked immunoassays for the detection of TIMP-1 (Kodama et al, 1989; Cooksley et al, 1990; Clark et a, 1991) and TIMP-2 (Fujimoto et a, 1993) have been described. These assays have been applied to body fluids, e.g. serum, plasma, amniotic fluid, cerebrospinal fluid, urine, but the number of samples tested has not been sufficient to establish normal ranges for TIMP levels in healthy individuals (Kodama et al., 1989; Clark et a, 1991). Furthermore, none of these assays has been sufficiently validated for technical performance or for clinical use.
In a study by Mimori et al (Mimori et al, 1997) in which tumor tissue levels of TIMP-1 mRNA were studied in patients with gastric carcinoma, high tumor/normal tissue ratios of TIMP-1 mRNA were found to be associated with increased invasion and poor prognosis. However, TIMP-1 protein levels in sera from prostate cancer patients and healthy donors (Baker et al, 1994) showed a high degree of overlap. Similarly, a separate study of plasma from prostate cancer patients and healthy donors showed no difference in TIMP-1 levels between the two groups (Jung et al, 1997).
Studies of TIMP-1 complexed with MMP-9 in plasma of patients with advanced gastrointestinal and gynaecological cancer (Zucker et al, 1995) demonstrated significantly higher levels in blood samples from cancer patients with metastatic disease compared to healthy control individuals, and that patients with high levels of TIMP-1:MMP-9 complex had a shorter survival (Zucker et al, 1995 and U.S. Pat. No. 5,324,634). However, this study did not include measurements of total or free TIMP-1, only the complex between TIMP-1 and one of the up to now approximately 24 identified MMP's. Furthermore, in this study, no differences in complex levels were found between patients with breast cancer and healthy donors. Also, this study did not include patients with early stage cancer.